The present invention relates generally to an improved field standard test weight, and more particularly to such a test weight utilizing a steel shell with a filling comprising a mixture of lead slag, metallic lead, and lead oxide. The individual components forming the fill are, of course, adjusted in accordance with established standards in order to achieve the required density of between 7 and 9 grams per cubic centimeter. For portability of the weight, it is desirable that the height be controlled within established limits.
In the past, test weights greater than 50 lbs., for example, have traditionally been made from a solid piece of cast iron. Traditional casting techniques normally provide a rejection rate of about 30 percent, the rejections being based upon the generation of blow-holes in the casting, thus contributing to under-weight units in the production. Because of the durability, cast iron had, in the past, been the accepted standard, particularly for those weights of 500 lbs. and above. For example, test weights of 1000 lbs. had a common and well-known size, that is, a solid having dimensions of 151/2 inches .times. 191/2 inches .times. 20 inches high.
For the traditional techniques of applying weight standards to commercial scales and the like, it has been common practice to utilize a plurality or group of 50 lb. test weights. These test weights are required for the calibration of certain commercial installations, and for continued administrative approval by various State, Federal and local agencies. The specifications and tolerances for field standard test weights are set forth in a publication by the National Bureau of Standards entitled "Specifications and Tolerances for Reference Standards and Field Standard Weights and Measures, (1) Specifications and Tolerances for Field Standard Weights (NBS Class F)", the publication being known as NBS Handbook 105-1, Revised 1972. This publication is available from the U.S. Department of Commerce, Superintendent of Documents, U.S. Government Printing Office, SD Catalog No. C 13.11:105-1. The publication is authored by Thomas M. Stabler of the Office of Weights and Measures, Institute for Applied Technology, National Bureau of Standards.
Typically, field standard test weights are constructed of materials such as steel or stainless steel having a hardness of Vickers 220 or greater, and are resistant to abrasion, denting and chipping. While cast iron is qualifying material, particularly for weights 20 lbs. and larger, production of such weights generates a significant number of rejects when the size becomes greater than 50 lbs., and particularly in sizes greater than 500 lbs. The density requirements for such field standard weights is between 7 and 9 grams per cubic centimeter.
While no particular form is required for the test weights, it has been determined that experienced personnel will utilize and recognize standard weights by size and configuration. Therefore, in order to reduce the likelihood of confusion, a standard form and size should preferably be retained, such as that set forth hereinabove for weights of 1000 lbs., for example. A standard configuration is also desired for reducing the likelihood of confusion, and also for aiding in portability, when desired.
In order to achieve a weight adjustment so as to render the test weight consistent with the tolerance level of one part in 10,000, a weight adjusting cavity is provided. In the present structure, such a weight adjusting cavity may be provided for receiving a fill of metallic lead, the density of the lead being sufficiently high so as to achieve an overall density of between 7 and 9 grams per cubic centimeter in the overall test weight.